The present invention relates to the technical field of an image recording apparatus and, more particularly, to a so-called dry printer that outputs a hardcopy by performing dry process (or dry developing process) on a recording material on which a diagnostic image read by a medical diagnostic image generating apparatus has been reproduced.
Medical diagnostic images taken by various types of the medical diagnostic image generating apparatuses utilizing techniques such as ultrasonography, computed tomography (CT), magnetic resonance imaging (MRI), radiography and computed radiography (CR) such as Fuji computed radiography (FCR) have conventionally been recorded on silver-salt photographic light-sensitive materials to produce hard copies.
However, the silver-salt photographic light-sensitive materials have the advantage of yielding high-quality images, but the wet development process thereof is time-consuming and laborious because of the necessity of the wet development process including color development, bleach-fix and wash, and the maintenance of developing machines such as wet-type processors is also a time-consuming job. Therefore, it is desired that hard copies are outputted by an image recording method which eliminates the need for wet process, namely, a method utilizing a dry printer, while using recording materials.
As the dry printer, a thermal recording apparatus using a thermal head or a heat-mode laser has been known.
Thermal recording uses a thermal head having a glaze in which heat-generating elements are arranged in one direction (i.e., main scanning direction). The respective heat-generating elements are heated in accordance with an image to be recorded, while moving the glaze and a thermal recording material relative to each other in the direction perpendicular to the main scanning direction, with the former being pressed on the latter. The thermal recording material is thus heated imagewise. On the other hand, in thermal recording in which a heat-mode laser is used, a thermal recording material containing a light absorbing agent and a light beam modulated in accordance with the image to be recorded are used. The thermal recording material is heated by being exposed imagewise by two-dimensional scanning with the thus modulated light beam whereupon the image is recorded thereon.
As the dry printer, an apparatus which performs image recording by means of exposing and thermal color forming, utilizing a light-sensitive and thermally developed recording material or a light-sensitive and thermal recording material has also been known.
Such apparatus, which uses, for example, a recording material containing an organic silver salt which produces a color by exposure and heating or another recording material containing a photo-curing agent and a heat-responsive microcapsule, records a latent image thereon by exposure and then changes the thus recorded latent image into a visible image by forming the color in either an exposed portion or unexposed portion thereof by heating whereupon the hardcopy having the visible image formed thereon is outputted.
In recent years, the quality of the image obtained by such dry printer has been significantly improved, and an extension of its use from recording of the conventional ultrasonic diagnostic image to other applications such as CT, MRI and radiography (CR) that require largesize and high-quality images has been reviewed and put to practical use.
Medical diagnosis to be performed by means of the image ordinarily uses a monochromatic image and is executed by viewing a fine structure from differences of densities in the image. Therefore, the medical diagnostic image is required to have extremely high sharpness (a high degree of sharpness).
Moreover, it is required in many cases that, in order to execute more accurate diagnosis, for example, as the diagnostic image of a chest or that used in orthopedics which has been taken by FCR (Fuji computed radiography), an image having a size equal to that of a subject, namely, an affected areas part, is to be outputted.
In this case, when the image having the size equal to that of the affected areas part is outputted, if a pixel size at the time of image reading (reading pixel density) with the diagnostic image generating apparatus such as FCR or the like and a recording pixel size (recording pixel density) in an image recording apparatus which outputs the diagnostic image as the hardcopy are different from each other, there exists a need for a magnification or a minification of the image by means of electronic magnification processing or electronic scaling.
For example, in a case that reading pixel density in the diagnostic image generating apparatus is 254 dpi (dots per inch) and the recording pixel density in the image recording apparatus is 300 dpi, sizes of pixels in the former density and latter density are 100 μm and 84.7 μm per pixel, respectively. In order to output the image having the size equal to that of the reading image, interpolation magnifying process, that is, multiplication of ca. 1.18 times, must be performed.
If the interpolation magnifying process multiplied by such non-integer is performed by means of spline interpolation or the like, frequency characteristics of the image are commonly deteriorated and, as a result, sharpness of the image is decreased; hence, the thus processed image is not preferable as a diagnostic image.
Moreover, if the interpolation magnifying process multiplied by the non-integer is performed on a replication, distortion of the image is clearly recognized visually; hence, the thus processed image is not preferable as the diagnostic image, either.
Furthermore, in the image recording by such dry printer as described above, the sharpness of the image is lower than that of the image in a silver-salt photography which has been subjected to wet process.
For example, in the thermal recording, a mechanism which develops a color by heating the thermal material to form an image thereon can not prevent developing the color in an area in which the color should not be primarily developed or generating an area in which a color of a higher density than a density originally aimed at is developed; as a result, sharpness of the image is decreased.
Moreover, in the image recording utilizing light, there is a decrease of sharpness due to halation (scattering, reflection or propagation of light). In wet-type image recording using the silver-salt photographic light-sensitive material, it is possible to add a substantial amount of halation inhibitor to the recording material since it is capable of being removed (washed) at the time of the wet process. Whereas, in the image recording by the dry printer, it is impossible to remove the halation inhibitor throughout the image forming process so that a sufficient amount of the halation inhibitor can not be added; as a result, there occurs decrease of sharpness of the image due to the halation. In addition to the above, in a recording material using microcapsules, reflection or scattering of light is brought about by the microcapsules whereupon decrease of sharpness of the image occurs.